We now reset the THD members related to auto_increment+binlog in
MYSQL_LOG::write(). This is better than in THD::cleanup_after_query(),
which was not able to distinguish between SELECT myfunc1(),myfunc2()
and INSERT INTO t SELECT myfunc1(),myfunc2() from a binlogging point
of view.
Rows_log_event::exec_event() now calls lex_start() instead of
mysql_init_query() because the latter now does too much (it resets
the binlog format).